It's 3M, and rated for 1kV underground AND submersible lines. Why wouldn't you trust it?
If it were something that Harbor Freight just started selling, I'd be with you, but 3M?

I too wonder how well it works. Polyolefin heat shrink is pretty abrasion resistant, and the stuff with the hot melt adhesive inside is quite waterproof.
I wonder if this is tacky on the inside, like the butyl adhesive on the underside of flashing tape. That would take care of the water issue.